Solar disinfection (SODIS) of viruses in PET bottles

Solar disinfection of drinking water in PET bottles (SODIS) is a simple point-of-use technique efficient for the inactivation of many bacterial pathogens. In contrast, the efficiency of SODIS toward viruses is not well known. In this work, we studied the inactivation of bacteriophages (MS2 and ɸX174) and human viruses (echovirus 11 and adenovirus type 2) by SODIS. We conducted experiments in PET bottles exposed to (simulated) sunlight at different temperatures (15, 22, 26 and 40°C) and in water sources of diverse composition and origin (India and Switzerland). Good inactivation of MS2 (more than 6-log inactivation after exposure to a total fluence of 1.34 kJ/cm2) was achieved in Swiss tap water at 22°C, while less efficient inactivation was observed in Indian waters and for echovirus (1.5-log at the same fluence). The DNA viruses studied, ɸX174 and adenovirus, were resistant to SODIS and the observed inactivation was equivalent to that occurring in the dark. Temperature enhanced MS2 inactivation substantially; at 40°C, a 3-log inactivation as achieved in Swiss tap water after exposure to a fluence of only 0.18 kJ/cm2. Overall, our findings demonstrate that SODIS may reduce the load of ssRNA viruses such as echoviruses, particularly at high temperatures and in photo-reactive matrices. In contrast, further complementary measures may be needed to ensure an efficient inactivation during SODIS of viruses resistant to oxidation such as ɸX174, or viruses undergoing rapid inactivation in the dark.